1. Field of the Invention
The present invention generally relates to a lubrication system for an engine, and more particularly relates to a lubrication system for an engine incorporating a balancer shaft.
2. Description of Related Art
Marine engines, such as those incorporated in outboard motors, are used to power a marine propulsion device. The propulsion device typically is a propeller and is submerged when an associated watercraft rests on a body of water. The engine typically is placed atop the outboard motor. A drive train and a transmission couple the engine with the propulsion device. Typically, the engine has a crankshaft extending generally vertically. The drive train includes a driveshaft disposed within a housing unit below the engine. The driveshaft also extends generally vertically and is connected to the crankshaft to transfer the power output from the engine to a propeller shaft which also is included in the drive train. The transmission couples the propeller shaft with the driveshaft.
Outboard motors are typically mounted on a transom of an associated watercraft so as to tilt about a tilt or “trim” axis. Occasionally, two or more outboard motors are mounted in parallel to a watercraft to provide more powerful propulsion.
The engine can incorporate a rotating balancer shaft that has a weight configured to counter-act vibrations from other moving parts of the engine. With respect to a balancer shaft, some specific considerations should be made in connection with the marine engines. For example, the balancer shaft should not interfere with the tilt movement of the outboard motor. Additionally, the balancer shaft of one outbaord motor should interfere with another outboard motor mounted in parallel thereto. Japanese Patent Publication No. 4-337143 discloses an exemplary layout of such a balancer shaft in a marine engine.
The balancer shaft can be journaled by bearings within the engine for rotation about a generally vertically extending axis and be disposed generally parallel to the crankshaft. The crankshaft drives the balancer shaft with a gear connection, for example. Due to being rotated in a relatively high speed, the bearings of the balancer shaft need to be sufficiently lubricated.
Typically, the engine is provided with a lubrication system to lubricate engine portions such as, for example, bearings of the crankshaft. For instance, if the engine operates on a four-cycle combustion principle, a closed-loop type lubrication system can be employed. Lubricant in this system is delivered to the engine portions that need lubrication by a lubricant pump and then returns back to a lubricant tank disposed below the engine by its own weight. A secondary lubrication system can be used to lubricate the balancer shaft bearings, independently of the other parts of the engine.